1 Technical Field
The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
2 Description of Related Art
Conventionally, there are known stators for electric rotating machines which include a hollow cylindrical stator core and a stator coil. The stator core has a plurality of slots that are formed in the radially inner surface of the stator core and spaced in the circumferential direction of the stator core. The stator coil is comprised of a plurality of electric wires mounted on the stator core.
Moreover, there is disclosed, for example in Japanese Patent Application Publication No. 2001-145286, a method of manufacturing a stator. According to the method, to improve the space factors of the electric wires in the slots of the stator core, each of the wires of the U-phase, V-phase, and W-phase windings of the stator coil is configured to have a rectangular cross section and have such an overall shape that when developed on a plane, the winding meanders in the form of cranks. Further, each of the U-phase, V-phase, and W-phase windings is wound by a predetermined number of turns into a spiral shape, so as to make the stator coil have a hollow cylindrical shape.
With the above method, however, each of the electric wires (or electric conductors) that respectively make up the U-phase, V-phase, and W-phase windings of the stator coil is required to have a long length. Accordingly, a large-scale shaping machine is needed for shaping the electric wires. Moreover, since each of the electric wires is long, it is difficult to handle the electric wires during the manufacture of the stator. As a result, it is difficult to secure a high productivity and a low cost of the stator.
To solve the above problems, the assignee of the present application (i.e., Denso Corporation) has developed a stator 20 as shown in FIG. 1. It should be noted that for the stator 20, the assignee of the present application has already applied for both a Japanese patent (application No. 2009-241798) and a U.S. patent (application Ser. No. 12/837,726).
The stator 20 includes a hollow cylindrical stator core 30 and a stator coil 40. The stator core 30 has, as shown in FIG. 2, a plurality of slots 31 that are formed in the radially inner surface of the stator core 30 and spaced in the circumferential direction of the stator core 30. The stator coil 40 is comprised of a plurality of electric wires mounted on the stator core 30.
Each of the electric wires has first, second, . . . , nth in-slot portions and first, second, . . . , (n−1)th turn portions, where n is an integer not less than 4. The first to the nth in-slot portions are sequentially received in p of the slots 31 of the stator core 30, where p is an integer not greater than n. The first to the (n−1)th turn portions are alternately located on opposite axial sides of the stator core 30 outside the slots 31 to connect corresponding adjacent pairs of the first to the nth in-slot portions. Each of the electric wires also has first and second end portions. The first end portion is closer to the first in-slot portion than any other of the in-slot portions of the electric wire; the second end portion is closer to the nth in-slot portion than any other of the in-slot portions of the electric wire. The first in-slot portions of the electric wires are located most radially outward and the nth in-slot portions are located most radially inward in the slots 31 of the stator core 30. Moreover, the stator coil 40 is a multi-phase (e.g., three-phase) stator coil that includes a plurality of phase windings. Each of the phase windings of the stator coil 40 is formed of at least two of the electric wires. The first end portion of one of the two electric wires is connected to the second end portion of the other electric wire.
With the above configuration, since each of the phase windings of the stator coil 40 is formed of the at least two electric wires, it is possible to shorten the length of each of the electric wires. Consequently, the electric wires can be shaped using a small-scale shaping machine and be easily handled during the manufacture of the stator 20. As a result, it is possible to achieve a high productivity and a low cost of the stator.
Moreover, in the stator 20, for each connected pair of the electric wires forming the stator coil 40, the first end portion of the one electric wire is connected to the second end portion of the other electric wire via an electrically-conductive crossover member 70. The crossover member 70 extends to cross over an annular coil end part 40A of the stator coil 40, which protrudes from an axial end face 30A of the stator core 30, from the radially inside to the radially outside of the coil end part 40A.
Furthermore, the crossover member 70 may be configured as an integral part of the second end portion of the other electric wire, as shown in FIG. 1. In this case, the first and second end portions of the pair of the electric wires are joined together by welding, forming a weld 70a therebetween.
However, with the above configuration, all the welds 70a between the first and second end portions of the connected pairs of the electric wires are located on the radially outer periphery of the stator coil 40 so as to be equally spaced in the circumferential direction of the stator core 30. Consequently, the spatial distances (or air clearances) d1 between the welds 70a become small, thereby making it difficult to ensure electrical insulation between the welds 70a. 